A GIS Database of Deep Sedimentary Temperatures in the Northern Continental Shelf of the Gulf of Mexico

Nagihara, Seiichi¹, Michael Smith² (1) Texas Tech University, Lubbock, TX (2) Minerals Management Service, New Orleans, LA

Bottom-hole temperature (BHT) data have been compiled from 371 boreholes distributed in the northern continental shelf of the Gulf of Mexico. The BHTs have been individually corrected for thermal disturbance associated with drill fluid circulation, and have yielded 577 estimates of the virgin-rock (or pre-drilling) temperature (VRT) in a depth range of 1 to 7 km sub-seafloor. The VRT estimates have been assembled into a database accessible by the geographic information systems (GIS) software, ArcGIS of ESRI. VRTs can be mapped and searched by specific geographic coordinates, lease block numbers, field names, API numbers, depth range, etc. Using this database, we have determined geothermal gradient at 35 localities in the continental shelf and spatially interpolated them to produce a continuous map for the continental shelf. Two geographic variation trends can be observed in the map. First, from east to west, geothermal gradient changes from medium (0.025 to 0.03 K/m) off Alabama and Mississippi to low (0.015 to 0.025 K/m) off eastern Louisiana, and to high and variable (0.03 to 0.06 K/m) off western Louisiana through Texas. Second, thermal gradient tends to be lower toward the outer continental shelf. Between the low geothermal gradient area off eastern Louisiana and the high gradient area off south Texas, there is a temperature difference of ~100° C at 5-km sub-seafloor depth. Such difference is large enough to cause regional variation in hydrocarbon maturation history and the bacterial and thermochemical sulfate reduction processes that yield hydrogen sulfide gas.